Existing control systems for oil-fired boilers furnishing steam to multiple apartment dwellings are operative to fire the boilers, and hence consume fuel oil, in accordance with boiler steam pressure. In practice, suitably spaced high and low steam pressure limits are established and sensed by pressure-sensitive electrical switch means. The boilers are fired where steam pressure falls below the low pressure limit and firing is discontinued when steam pressure rises to the high pressure limit. These existing control systems direct such boiler firing by connecting, in series circuit with such switch means, a magnetic line starter or the like which supplies electrical power to the oil-firing systems of each of the participating boilers. When the switch means provides electrical continuity therethrough, each oil-firing system is then operated if the sensing devices thereof, i.e., flame detector, low water detector, and the like, indicate that conditions particular to the boiler associated therewith are proper.
This so-called "pressure demand" control system, or equivalent system monitoring high and low limits of steam characteristics indicative of the stored heat content thereof, has no more than a coarse capacity for monitoring dwelling heat losses, i.e., to the extent that a decrease in the measured steam characteristic correlates generally with some heat loss. Actual dwelling temperature comfort control is effected, however, by valve means responsive to an auxiliary control system for regulating the flow of generated steam from the boilers to the dwelling.
While the functional independence of the pressure demand control system and such auxiliary temperature-based control system is necessary, the arrangement does not adapt itself particularly well to energy conservation. Thus, occasions arise where the former system calls for firing boilers while the latter system concurrently calls for a reduction in the supply of steam to the dwelling.